Method for the transmission of data packets in a mobile radio system and corresponding mobile radio system

ABSTRACT

A method transmits data packets in a mobile radio system and corresponding mobile radio system. The method permits an immediate transmission of data packets to the receiver station along a new transmission path, after a handover of a connection along a transmission path, between a transmission station and a receiver station, to a new transmitting station. The new transmission station thus receives no information regarding the transmission status of data packets, which were transmitted before the handover of the connection.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/EP2003/006394 filed on Jun. 17, 2003, GermanApplication No. 102 30 400.9 filed on Jul. 5, 2002 and EuropeanApplication No. 02015083.5 filed on Jul. 5, 2002, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for the transmission of data packetsin a mobile radio system, and a corresponding mobile radio system.

In mobile radio systems such as GSM (Global System for Mobilecommunications) and UMTS (Universal Mobile Telecommunications System)data and data packets are transmitted from the fixed network bytransmission stations to receiver stations by way of an air interface.FIG. 1 shows a known UMTS in schematic and simplified form. The fixednetwork CN is connected by data lines Iu to the UTRAN (UniversalTerrestrial Radio Access Network). The UTRAN comprises a plurality ofsubsystems RNS (Radio Network Subsystem) which each have a data line Iuto the fixed network CN. Always connected to each data line Iu is acontroller RNC (Radio Network Controller) which is in turn connected byconnections Iub to a plurality of base stations B. A plurality of cellsof the mobile radio system can be assigned to each base station B (e.g.by way of sector antennas). The interface between UTRAN and the userequipment UE which is referred to in GSM as a mobile station isimplemented by way of the interface Uu by a radio link. The controllersRNC of different subsystems RNS are as a rule connected by a furtherinterface Iur. This further interface Iur is required for a so-calledhandover (switch of cell), amongst other things.

During a soft handover, the user equipment UE is simultaneouslyconnected to at least two base stations B which are each capable ofbeing assigned to different controllers RNC. Since only one connectionIu is required in order to exchange data between user equipment UE andfixed network CN, the data flow is controlled by only one controllerRNC, called SRNC (Serving RNC). If the two base stations B are to beassigned to different controllers RNC, only one of the controllers RNCis the SRNC, while the second controller is referred to as the DRNC(Drift RNC). The controller known as DRNC handles its data transmissionto and from the fixed network CN by way of the further interface Iur andthus by way of the controller SRNC.

In each controller RNC, a connection check RLC (Radio Link Control) isperformed with the aid of a storage facility RS in which, apart from thedata packets, information is stored concerning which data has been sent,is to be sent again, or is yet to be sent. In the case of a softhandover, this data transmission status information is however storedonly in the controller SRNC. The user equipment UE also has a similarstorage facility US for status information and data packets, whichstores information about which data it has successfully decoded and forwhich data it is requesting a re-transmission. In the event ofsuccessful decoding of the data, the user equipment UE sends aconfirmation ACK (acknowledge) to the radio link control RLC facilityfor the relevant controller RNC. If the decoding is not successful, aNACK (non acknowledge) is sent instead.

Whereas during the soft handover a connection exists simultaneouslybetween the user equipment UE and at least two base stations B, duringthe hard handover the connection is only transferred from one basestation B to another base station B if the connection to the first basestation B has been previously terminated. Just as in the case of thesoft handover, this connection handover can take place both between basestations B of one and the same controller RNC and also between basestations B of different controllers RNC. Following a hard handover,however, a synchronization of the stored data transmission statusinformation must take place between the user equipment UE and therelevant controller RNC and, where necessary, the storage contents ofthe old controller RNC must be transmitted to the new controller RNC.This synchronization of the data transmission status information takestime and delays the resumption of data transmission following a hardhandover. High data transfer rates cannot therefore be achieved in thismanner.

The same holds true in respect of the data transfer rate in the case ofa fast selection of the radio cell with which the user equipment UEwishes to operate a connection. The user equipment UE has a set of radiocells for possible selection by way of which it can route the connectionto the fixed network CN. The user equipment UE then determines the radiocell having the best properties and signals in the uplink direction thecell from which it wishes to be supplied. This principle is referred toas Fast Cell Selection (FCS). If the chosen cell changes during aconnection, then the same problem occurs with FCS as in the case of ahard handover. The synchronization of the stored data transmissionstatus information must also take place for FCS as described in theprevious paragraph. High data transfer rates are not therefore possiblein this manner even in the case of FCS.

Future mobile communication systems will however require, and need tosupport, high data transfer rates. One example of this is High SpeedDownlink Packet Access (HSDPA) which is currently under discussion bythe 3rd Generation Partnership Project (3GPP) for UTRA FDD and TDD(Universal Terrestrial Radio Access Frequency Division Duplex and TimeDivision Duplex). In order to achieve high data transfer rates, controlof the data transmission is shifted from the controller RNC into thebase stations B, in other words in the base stations B additionalstorage facilities BS are set up which store the data packets and thedata transmission status information. Time savings are achieved in thisway since the transmission path between the controller RNC and the basestations B is dispensed with during control of the data transmission.Even when this new storage facility BS is included in the base stationsB the hard handover takes place as described previously. Proposals onthis topic may be found for example in a paper presented by Motorola onthe occasion of the TSG-RAN Working Group 2 meeting #18/00 in Edinburgh,15 to 19 Jan. 2000, under the title “Fast Cell Selection and Handoversin HSDPA” (R2-A010017). As explained above, the data transmission isresumed when the new base station B has been informed of the status ofthe data transmission, in other words when the storage contents of theold base station B have been sent to the new base station B. Thissynchronization of the data transmission status information between oldand new base station B takes place in this situation either by way ofthe connections Iub on the controller RNC and if applicable also by wayof the further interface Iur and/or by the user equipment UE by way ofthe radio interface. The limits for HSDPA are thus given as a result ofthe finite time which is required for transmission of the storagecontents of the old base station B (data packets and transmission statusof the data packets) to the storage facility BS of the new base stationB.

A handover from an old base station to a new base station for a cellularcomputer device is described in EP0695053A. The protocol status for thedata transmission is notified to the new base station either byappropriate information from the cellular computer device, informationfrom the old base station or a combination of information from bothsources during the handover.

A method for operating a mobile radio network is described in DE 100 17062 A1, whereby in the case of a switch of connection for a mobilestation from a first base station to a second base stationtransmission-specific information is transmitted from a firsthigher-level network unit to a second higher-level network unit in orderto resume a transmission of data units to the mobile station after theswitch in connection from the current status.

SUMMARY OF THE INVENTION

One possible object of the invention is therefore to set down a methodwhich in the event of a change of cell assigned to the user equipment UE(hard handover or FCS) allows a higher data transfer rate to be achievedthan has previously been possible.

With regard to the method for the transmission of data packets from afirst transmission station to a mobile receiver station in a mobileradio system, a connection is established between the first transmissionstation and the receiver station by way of a second transmission stationand first data packets are sent from the first transmission station tothe second transmission station for transmission to the receiverstation. Information relating to those first data packets which have notbeen successfully transmitted by way of the second transmission stationto the receiver station is determined in the second transmission stationand/or the receiver station. This information thus provides statusinformation for the data transmission. A handover of the connection to athird transmission station takes place and after the handover of theconnection second data packets are sent from the first transmissionstation to the third transmission station and transmitted from there tothe receiver station. The information relating to those first datapackets which have not been successfully transmitted by way of thesecond transmission station to the receiver station is sent to the firsttransmission station and/or the third transmission station only aftertransmission of the second data packets. This method makes it possiblein the event of a switch of connection, as occurs as a result of ahandover or a fast cell selection process, to transmit data packetsimmediately without the third transmission station and/or the firsttransmission station having knowledge of the success or lack of successin relation to previously transmitted data packets, in other words hasat its disposal the data transmission status information ascertainedfrom the second transmission station and/or the receiver station. Themethod is able to guarantee higher data transfer rates in the event of aswitch of connection than is possible when prior to the resumption ofthe data transmission the data transmission status information is firstsent from the second transmission station to the third transmissionstation and/or the first transmission station. In particular, thismethod is suitable for data transmissions having high data transferrates such as High Speed Downlink Packet Access (HSDPA).

In a first embodiment, the method is implemented in a cellular mobileradio system. In this case, the first transmission station is acontroller, the second and third transmission stations are base stationsand the receiver station is a user equipment.

A second embodiment implements the method in an ad-hoc network (alsoknown as self-organizing network). In an ad-hoc network, in other wordsa communication network which can also be formed exclusively usingmobile stations, the first transmission station is a mobile station oran access station. In this situation, an access station is understood tobe a fixed station which allows access to the fixed network. The secondand third transmission stations and also the receiver station are mobilestations.

By preference, the second data packets do not match any of the firstdata packets. This course of action serves to ensure that no datapackets are transmitted more than once. This again increases the datatransfer rate during the switch of connection.

In an alternative embodiment, the second data packets match those of thefirst data packets which although sent from the first transmissionstation to the second transmission station have however no longer beentransmitted from the second transmission station to the receiver stationprior to handover of the connection. When using this embodiment, datapackets which the user equipment should already have received during thedata transmission by the first transmission station are transmittedimmediately on handover of the connection. These data packets then reachthe user equipment for the first time and this happens before the thirdtransmission station is aware of the status of the data transmission.The data transfer rate is thus increased for its part.

It is advantageous to determine on the basis of the probable duration oftransmission from the first transmission station to the secondtransmission station or to the receiver station those of the first datapackets which although sent from the first transmission station to thesecond transmission station have however no longer been transmitted fromthe second transmission station to the receiver station prior tohandover of the connection. On the basis of the probable duration oftransmission, in other words on the basis of the time which a datapacket requires in order to be received by the second transmissionstation or by the receiver station after being sent by the firsttransmission station, the first transmission station can specify whichdata packets were never able to reach the receiver station although theywere sent by the first transmission station before the switch ofconnection was carried out. These data packets can then be transmittedby the third transmission station without this transmission stationhaving data transmission status information.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 shows a UMTS according to the related art,

FIG. 2 shows a section of a cellular mobile radio system according toone embodiment of the invention,

FIGS. 3 to 7 show the manner of execution of data transmission during aswitch in connection, and

FIG. 8 shows a different embodiment of the mobile radio system accordingto one embodiment of the invention, in the form of an ad-hoc network.

The invention will be described in the following with reference to aUMTS. The invention can naturally also be used for other mobile radiosystems. This applies in particular to GSM, ad-hoc networks (see FIG. 8)and 4th generation mobile radio systems.

The same reference characters in FIGS. 1 and 2 denote the same objects.

The section of a UTMS illustrated in FIG. 2 shows a first, a second anda third transmission station represented by a controller RNC, a firstbase station B1 and a second base station B2. A connection existsbetween a receiver station taking the form of a user equipment UE andthe first base station B1 by way of a transmission path 1. First datapackets DPm are transmitted over this connection from the fixed networkCN by the interfaces Iu and Iub1 to the user equipment UE. Thecontroller RNC has a storage facility RS. The base stations B1, B2having storage facilities BS and the user equipment UE having a storagefacility US have a processor P which is used to determine theinformation I described below. The storage facilities RS, BS, US areused for storing data packets and information relating to the datatransmission status for each data packet.

In the first base station B1 the data packets DPm sent by the controllerRNC are stored in the storage facility BS and transmitted from there tothe user equipment UE. In this situation, in the first base station B1and in the user equipment UE the information I that specifies which ofthe first data packets DPm have not been successfully transmitted by wayof the first base station B1 to the user equipment UE is determined bythe processor P. This information I thus specifies for which of thefirst data packets DPm a NACK signal has been sent by the user equipmentUE to the first base station B1 and which of the first data packets DPmhave not yet been transmitted to the user equipment UE although theyhave been transmitted by the controller RNC to the first base stationB1. The controller RNC can ascertain on the basis of the contents of itsstorage facility RS which data packets it has already sent to the firstbase station B1 and which data packets it has not yet sent to the firstbase station B1.

If the connection quality of the connection over the transmission path 1falls below a minimum level while a better connection quality ispossible at the same time for a potential transmission path 2 by way ofthe second base station B2, then a switch in transmission path takesplace, in other words the connection is handed over from the first basestation B1 to the second base station B2. Immediately after thishandover, second data packets DPm′ are already being sent by thecontroller RNC to the second base station B2 and transmitted from thereto the user equipment UE. These second data packets DPm′ have not beenpreviously sent to the first base station B1. The controller RNC canensure that this happens in that, on the basis of the transmissionstatus of its storage facility RS, it sends only second data packetsDPm′ having identification numbers m′ from its storage facility RS whichit has not previously sent to the first base station B1. In this manner,a data transmission to the user equipment UE is already enabled againimmediately after the handover. Only after or during the transmission ofthese second data packets DPm′ to the user equipment UE is the secondbase station B2 informed about those of the first data packets DPm whichhave previously not been successfully transmitted by way of the firstbase station B1 to the user equipment UE, in other words for which theuser equipment UE has sent a NACK signal to the first base station B1,or which have been stored in the first base station B1 but have not yetbeen transmitted to the user equipment UE. To this end, this informationI is sent by the user equipment UE by way of the air interface and bythe first base station B1 by way of the interfaces Iub1 and Iub2 to thesecond base station B2. After the information I has been sent and thedata packets designated by the information I have been transmitted atthe same time by way of the interfaces Iub1 and Iub2, the datatransmission of these data packets is performed subsequently and themobile radio system resumes the normal data transmission.

The timing sequence of the data transmission before and shortly afterthe connection handover from the first base station B1 to the secondbase station B2 is described in FIGS. 3 to 7. The tables show thecontents of the storage facilities RS, BS, US of the stations involvedat different points in time. The first column (new) for the storagefacility RS of the controller RNC lists identification numbers of thosedata packets which the controller RNC has received from the fixednetwork CN but has not yet sent to the storage facility BS of the firstbase station B1 or of the second base station B2. The first column (new)for the storage facility BS of the first base station B1 and of thesecond base station B2 in each case contains identification numbers ofthose data packets which have been received by the controller RNC buthave not yet been sent to the user equipment UE. The second column(sent) for the storage facilities RS, BS in each case gives theidentification numbers of data packets which have already been sent,while the third column (retrans) contains identification numbers of datapackets which have been re-transmitted following a NACK signal. In thestorage facility US for the user equipment UE, the first column (ACK)indicates which data packets have been successfully decoded, while thesecond column (NACK) contains those identification numbers whoseassociated data packets could not be successfully decoded and for whicha re-transmission is requested. In the following, the specification“data packet n” denotes the data packet having the identification numbern.

According to FIG. 3, during the connection using transmission path 1 thecontroller RNC initially sends data packets 1 to 4 (sent) as first datapackets DPm (cf. FIG. 2) to the first base station B1. Further datapackets 5 to 9 (new) are still contained in the queue and are waiting tobe sent. The first base station B1 has already transmitted data packets1 to 3 (sent), while although data packet 4 has been received it has notyet been transmitted to the user equipment UE. The user equipment UE hassuccessfully decoded data packets 1 and 3 (ACK), but data packet 2 hasnot been received successfully (NACK) and a re-transmission isrequested.

In order to give a better overview, a further transmission of new datapackets parallel to the updating of the storage contents is not alwaysshown in the following figures. This parallel transmission is possible,however.

In FIG. 4, the storage facility RS for the controller RNC remainsunchanged. After the transmission of ACK signals and NACK signals fromthe user equipment UE to the base station B1, the data packet 4 stillremains available for transmission in the first base station B1, but hasnot yet been sent. The base station B1 is then informed about the factthat the data packet 2 needs to be re-transmitted (retrans). This datapacket 2 has not yet been successfully received by the user equipmentUE, with the result that the status “NACK” remains stored for this datapacket. The information relating to the status “ACK” for the datapackets 1 and 3 is no longer required and has been deleted in themeantime.

If the handover takes place in this state, this then results in thesituation shown in FIG. 5. The storage facilities of the first basestation B1 and of the user equipment UE remain unchanged. However, newdata packets 5 to 7 (sent) are already being sent by the controller RNCas second data packets DPm′ (cf. FIG. 2) to the second base station B2(see there in the first column). The question marks in the columns ofthe second base station B2 indicate that the second base station B2 hasno information whatsoever at this point in time relating to the mannerof execution of the previous transmission (transmission path 1 in FIG.2).

In FIG. 6, a transmission of the data packets 5 to 7 (sent) is thenalready performed by the second base station B2, while at the same timeor following this transmission the storage facilities of the first basestation B1 and of the user equipment UE are synchronized with the secondbase station B2 (status synchronization). During the statussynchronization, both the data transmission status information stored asinformation I in the storage facility BS of the first base station B1 issynchronized and the necessary data packets are also transmitted. Inthis example the data packets 2 and 4 as well as the associated statusinformation (information I) are therefore transmitted during the statussynchronization. In this situation, the storage facility of the userequipment UE naturally already contains information relating to thesuccess in transmitting the data packets 5 to 7, in addition to thestatus information which is still stored there for data packet 2.

After the updating of the storage facility of the second base stationB2, the storage status of the first base station B1 (see FIG. 7) isaccordingly contained therein, in other words the data packet 4 in thefirst column and the data packet 2 in the third column. Similarly, thethird column contains the data packet 6 for which the user equipment UEhas requested a re-transmission.

According to one aspect of the invention, first data packets 5 to 7 arethus initially transmitted by way of the second base station B2 beforethe status synchronization takes place. When compared with this,according to the related art the transmission of the data packets 5 to 7would not take place until after the status synchronization.

The first base station B1 and the second base station B2 are assigned toonly a single controller RNC in the embodiment illustrated. However, themethod can also be applied to situations in which the first base stationB1 and the second base station B2 belong to different controllers RNC(cf. FIG. 2). In this case, the interface Iur is additionally requiredduring the status synchronization.

In a further embodiment, the controller RNC knows the probabletransmission time for data packets to reach the first base station B1 orto reach the user equipment UE. It can thus calculate or estimatewhether the data packet 4 could have been transmitted to the userequipment UE prior to the handover. If the result is that atransmission, as can be seen from FIG. 5 for the data packet 4, wasunable to take place prior to the handover, then the controller RNC cannaturally actually send the data packet 4 together with the data packets5 to 7 and thus additionally increases the data transfer rate during theswitch of connection. This case is represented by the digit 4 withinparentheses in the storage facility BS of the second base station B2.The controller RNC can determine the probable transmission time from themaximum data transfer rate for the transmission of the first datapackets DPm from the first base station B1 to the user equipment UE andfrom the delay in sending the first data packets DPm from the controllerRNC to the first base station B1. The delay in sending to the first basestation B1 is known to the controller RNC as a result of the previoussend process and can be approximately 10 to 100 milliseconds. In thissituation, large delay times are obtained in particular in cases whenthe interface Iur is required for sending data packets, in other wordswhen different controllers RNC are involved in the data transmission.For example, if a probable transmission time of 100 millisecondsresults, then the controller RNC can assume that data packets which ithas sent to the first base station B1 80 milliseconds (100 millisecondsless a safety margin of 20 milliseconds in this example) prior to thehandover were no longer able to be transmitted to the user equipment UE.The controller RNC can send these data packets together with datapackets which have not yet been sent to the first base station B1immediately to the second base station B2.

The method can also be used in an ad-hoc network, as is represented inFIG. 8. In this case, the first data packets DPm are either sent from afirst mobile station MS1 or an access station ZS to a second mobilestation MS2 and transmitted from there to a further mobile station MS4as a receiver station. The second data packets DPm′ are sent to a thirdmobile station MS3 and transmitted from there to the further mobilestation MS4. With regard to an access station, this is a fixed stationwhich—in similar fashion to the controller RNC in UMTS—grants the userstations of an ad-hoc network access to the fixed network CN. Mobilestations MSi each have a storage facility S for data packets and datatransmission status information and a processor P for determining theinformation I. Apart from different designations for the transmissionstations and the receiver station, the manner of execution of the methodin an ad-hoc network, as is represented in FIG. 8, is identical to theembodiment described previously with reference to a cellular system(FIGS. 2 to 7).

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention.

1. A method for the transmission of data packets from a firsttransmission station to a mobile receiver station in a mobile radiosystem, comprising: establishing a connection between the firsttransmission station and the mobile receiver station by way of a secondtransmission station, sending first data packets from the firsttransmission station to the second transmission station for transmissionfrom the second transmission station to the mobile receiver station,determining information relating to first data packets which were notsuccessfully transmitted to the mobile receiver station, the informationbeing determined in the second transmission station and/or the mobilereceiver station, performing a handover of the connection from thesecond transmission station to a third transmission station, after thehandover of the connection, transmitting second data packets from thefirst transmission station to the mobile receiver station via the thirdtransmission station, and sending the information to the firsttransmission station and/or the third transmission station only aftersecond data packets are transmitted.
 2. The method according to claim 1,wherein the method is implemented in a cellular mobile radio system, thefirst transmission station is a controller, the second and thirdtransmission stations are base stations, and the mobile receiver stationis a user equipment.
 3. The method according to claim 1, wherein themethod is implemented in an ad-hoc network, the first transmissionstation is a mobile station or an access station, and the second andthird transmission stations are mobile stations.
 4. The method accordingto claim 1, wherein the second data packets do not match any of thefirst data packets.
 5. The method according to claim 1, wherein thehandover occurs before all of the first packets are transmitted from thesecond transmission station to the mobile receiver station, therebyleaving remaining first packets; the second data packets include datapackets that match the remaining first data packets.
 6. The methodaccording to claim 5, wherein the remaining first data packets are notsuccessfully transmitted from the second transmission station to themobile receiver station after the handover.
 7. The method according toclaim 5, wherein the remaining first data packets are identified on thebasis of a probable duration of transmission from the first transmissionstation to the second transmission station or from the firsttransmission station to the mobile receiver station, and afteridentification, the remaining first data packets are sent to the mobilereceiver station as second data packets.
 8. The method according toclaim 7, wherein the remaining first data packets are identified in thefirst transmission station.
 9. The method according to claim 1, furthercomprising successfully receiving pre-handover packets at the mobilereceiver station, the pre-handover packets being sent from the firsttransmission station via the second transmission station.
 10. The methodaccording to claim 1, further comprising sending post-handover packetsafter sending the information, the post-handover packets being sent fromthe first transmission to the mobile receiver station via the thirdtransmission station.
 11. The method according to claim 1, wherein thehandover is a hard handover.
 12. The method according to claim 1,wherein the handover is part of a Fast Cell Selection process.
 13. Themethod according to claim 1, wherein the first data packets which werenot successfully transmitted to the mobile receiver station comprise:packets that were transmitted to the second transmission station, butwere not transmitted from the second transmission station to the mobilereceiver station before the handover; and packets for which the mobilereceiver station has sent a NACK signal.
 14. The method according toclaim 3, wherein the second data packets do not match any of the firstdata packets.
 15. The method according to claim 3, wherein the handoveroccurs before all of the first packets are transmitted from the secondtransmission station to the mobile receiver station, thereby leavingremaining first packets; the second data packets include data packetsthat match the remaining first data packets.
 16. The method according toclaim 15, wherein the remaining first data packets are not successfullytransmitted from the second transmission station to the mobile receiverstation after the handover.
 17. The method according to claim 16,wherein the remaining first data packets are identified on the basis ofa probable duration of transmission from the first transmission stationto the second transmission station or from the first transmissionstation to the mobile receiver station, and after identification, theremaining first data packets are sent to the mobile receiver station assecond data packets.
 18. A mobile radio system, comprising: a firsttransmission station; a second transmission station to receive firstdata packets from the first transmission station; a mobile receiverstation to receive first data packets from the first transmissionstation via a connection through the second transmission station; athird transmission station to receive second data packets after ahandover of the connection from the second transmission station to thethird transmission station, the second data packets being received fromthe first transmission station for transmission to the mobile receiverstation; a checking unit to determine information about first datapackets that were not successfully transmitted to the mobile receiverstation by way of the second transmission station, the checking unitbeing provided in the second transmission station and/or the mobilereceiver station; and an information send unit to send the informationto the first transmission station and/or the third transmission stationonly after the handover of the connection to the third transmissionstation has taken place and second data packets have been sent from thefirst transmission station to the third transmission station.
 19. Thesystem according to claim 18, wherein the information send unit sendsthe information only after the second data packets have been transmittedfrom the third transmission station to the mobile receiver station. 20.The system according to claim 18, wherein pre-handover packets aresuccessfully received at the mobile receiver station, the pre-handoverpackets being sent from the first transmission station via the secondtransmission station.
 21. The system according to claim 18, whereinpost-handover packets are sent after sending the information, thepost-handover packets being sent from the first transmission to themobile receiver station via the third transmission station.
 22. Thesystem according to claim 18, wherein the handover is a hard handover.23. The system according to claim 18, wherein the handover is part of aFast Cell Selection process.
 24. The system according to claim 18,wherein the first data packets which that not successfully transmittedto the mobile receiver station comprise: packets that were transmittedto the second transmission station, but were not transmitted from thesecond transmission station to the mobile receiver station before thehandover; packets for which the mobile receiver station has sent a NACKsignal.
 25. The system according to claim 18, wherein the firsttransmission station is a controller, the second and third transmissionstations are base stations, and the mobile receiver station is a userequipment.
 26. The system according to claim 18, wherein the system ispart of an ad-hoc network, the first transmission station is a mobilestation or an access station, and the second and third transmissionstations are mobile stations.
 27. The system according to claim 18,wherein the second data packets do not match any of the first datapackets.
 28. The system according to claim 18, wherein the handoveroccurs before all of the first packets are transmitted from the secondtransmission station to the mobile receiver station, thereby leavingremaining first packets; the second data packets include data packetsthat match the remaining first data packets.
 29. The system according toclaim 28, wherein the remaining first data packets are not successfullytransmitted from the second transmission station to the mobile receiverstation after the handover.
 30. The system according to claim 18,wherein the remaining first data packets are identified on the basis ofa probable duration of transmission from the first transmission stationto the second transmission station or from the first transmissionstation to the mobile receiver station, and after identification, theremaining first data packets are sent to the mobile receiver station assecond data packets.
 31. The system according to claim 30, wherein theremaining first data packets are identified in the first transmissionstation.